It is well known that the operative working tools of machine tools, such as drills of drilling machinery or cutting tools of lathes, shaping-and milling machines require constant cooling when working on metal workpieces. Generally the cooling is effected by feeding a coolant, such as an acqueous soap solution or oil to the tool. Many arrangements for feeding the coolant to the working tool have been proposed, some more and some less effective, but none being fully satisfactory, in view of certain technical difficulties inherent to the respective metal working processes. Especially, in the case of working tools held in spring collet chucks (such as generally employed for precision work) the cooling of the tool presented some difficulty.